This meteorological transmitter was found to be located in the open on
land, and serves a purpose similar to the larger, floating meteorological stations
known to be used by the enemy.
The full equipment comprises a complete low-power, short-wave
transmitter, automatically operated by meteorological instruments, to record
the temperature and pressure in the locality in which it is stationed. The
times and periods of transmission are set on a master clock.
The transmitter is a Lorenz crystal-controlled, four-tube transmitter
made in 1940, operating over two wave bands: 17.5 to 6.6 and 6.6 to 5.6
megacycles per second. The tubes are master oscillator, frequency-doubler, and
two 15-watt output tubes, in what appears to be a push-pull circuit. Continuous
wave or interrupted continuous wave can be transmitted when the transmitter
is switched on by the clock mechanism. This transmitter is obviously a
factory production and is well mounted in a tubular frame, but the whole is
encased in a weatherproof container of doubtful efficiency and "workshop"
finish. The clock unit was also in this container, but was sealed in its
case with a waxed-wood cover and a waterproof packing.
The meteorological controlling unit is a Morse-sending device; the signals
sent being altered by the positions of three contactors, and the contactors
being moved by the meteorological instruments. In addition, a further contactor
is hand-set, presumably to pick out the recognition signal of the meteorological
station. The operating meteorological devices consist of a curved bi-metallic
strip for registering the temperature, and two barometers, one with twin capsules
(coarse reading), and the second with four barometric capsules (fine reading). It
is necessary to provide two barometric devices in order that the full reading
may be obtained. It is thought that the first instrument will transmit a signal
indicating the nearest millimeter, and the second will provide the decimal part
of the local pressure reading. The contactors, operated by a geared-up
rack-and-pinion movement, are in the form of 10-finger stars with sharpened
points, arranged around the circumference of a circle. The result of a change of
temperature or pressure is to alter the position of these points relative to the
axis of this circle. The rotor, or contact arm on which these contactors
operate, consists of a sector-shaped piece, the circumference of which moves
around the circle inscribed by the contactors. The sequence is that the sector
first makes contact with the identification signal, then with the coarse
barometer, the fine barometer, and finally, the thermometer contactor.
It should be understood that, according to the setting of the contactors, a
different signal is picked up by the projecting fingers. Anyone receiving this
signal can ascertain the position of the contactor, and hence the temperature or
pressure at the moment of transmission, if the key of the coding on the rotor
arm is available.
The clock is an elaborate mechanism for performing the simple task of
making contact between two leads for the periods of transmission. It consists
of an electrically wound clock which registers the time by means of a rotating
disk, engraved with the 24 hours. The switch operating devices are secured by
means of two thumbscrews around the periphery of this disk. The two
leads, "shorted" by the clock, switch on the transmitter and meteorological unit. There
are two batteries in the set: one a 24-volt, 69-ampere hour, low-voltage
unit, contained in a weather proof metal case, 3 feet 6 inches by 1 foot square; the
other, a high-voltage battery consisting of four 90-volt cells connected in
series. The latter was of similar type and construction but
of 11-ampere hour capacity.